Seven solar-powered stations were buried in the Greenland ice sheet to detect neutrinos, but they ended up detecting solar flares from the Sun itself

Small solar panels power stations, with antennas that dip into frozen darkness across Greenland’s ice sheet. They are designed to detect radio flashes from ultra-high-energy neutrinos that traverse the ice.

However, information gathered from two summers in the Arctic kept coming in waves during the Sun’s activity. The instruments were not broken and the observatory had a new scientific purpose.

How did equipment designed to go under the ice hear eruptions coming from the sky?

Engineers could compare the reconstructed direction with the Sun’s position to verify the array’s pointing accuracy to less than one degree.

The story of how seven stations started listening under Greenland

Construction of the Radio Neutrino Observatory in Greenland, RNO-G, started in 2021 near Summit Station.

In 2022, four additional stations were installed and three in 2021. 24 antennas were installed near the surface and in three deep boreholes, which were combined at each station.

Several antennas were placed in shallow trenches. Others plunged about 330 feet down to intercept radio signals that were passing through a thick layer of ice.

Each station was equipped with solar panels and batteries, enabling them to function independently during the brighter months of the polar year. Power stored kept operations going into the fall.

The primary goal was to capture a short radio pulse that formed following an extremely energetic neutrino interacting within the ice.

Such particles rarely collide with matter. That makes them valuable cosmic messengers, but extremely difficult to catch.

The planned grid for RNO-G will eventually have 35 stations distributed throughout the ice. During the solar study, seven were listening.

They were very sensitive and picked up any pulse rising above the background. That openness led to an unplanned route into solar physics.

The activity was well above the ice with the signal spikes

This peculiar pattern was observed in the data gathered in the summers of 2022 and 2023.

A few solar observatories reported radio flares, which led to increases in trigger rates at several stations. One detector might have been disturbed by local machinery, but coordinated spikes were more difficult to explain away.

They found 75 flares that led to statistically significant trigger increases.

RNO-G also handled about 60 percent of the brightest relevant events observed by a satellite instrument.

The signals were very brief radio pulses. RNO-G’s fine time structure was recorded much more quickly than many dedicated solar observatories.

The capability might be useful to researchers in the study of flare emission changes with frequency and time. It also provided the neutrino team with a known position source.

Engineers could compare the reconstructed direction with the Sun’s position to verify the array’s pointing accuracy to less than one degree.

The secret was to be found within the design of the equipment itself. The range of frequencies selected to detect the neutrinos from the sun also included a portion of the Sun’s radio voice.

The detail that links the buried antennas to the Sun

The solar flares reached RNO-G because they produce a powerful radio burst at the same frequency band that is listened to for neutrino events.

The stations tune in between about 80 megahertz and 700 megahertz. In some flares, the radio emission is generated by the accelerated electrons and the moving shock fronts over that range.

The RNO-G triggers are near the normal thermal-noise floor. If the solar burst is bright enough, then it passes the recording threshold, and no neutrino triggers it.

This effect is enhanced by the near surface antennas being several pointing up. They are more efficient at receiving signals from above than the deeper antennas.

There’s another neat coincidence with solar energy. Most stations collect data during the Arctic daylight season when the Sun is visible for extended periods.

The solar panels are not responsible for flare detections. They just keep the observatory running as the same star transmits radio waves to Greenland.

What the flare detections do and do not mean

The outcome is not that the stations gave up on their actual mission.

Neutrinos with very high energies are very rare, and RNO-G is still a growing discovery machine. Solar bursts are not targets, they are additional signals.

It is important to also detect those bursts before interpreting other events, which is where the researchers come in. But the Sun provides an unusually practical calibration source.

Its location is known and a strong flare is seen at separate stations nearly simultaneously. Engineers can then test the timing, the hardware response, and the reconstructed direction.

The original analysis was for 7 stations. The project is reporting 8 stations deployed by July 2026, and construction is underway for 35 stations.

RNO-G is not looking for solar neutrinos, but for radio emission generated during solar activity. A misplaced signal turned into a reliable systems check.

Now there are two versions of the Sun in the scene on Greenland’s ice.

Its normal light illuminates the solar panels and keeps the remote electronics functioning. Radio energy is used to test the accuracy of the antennas during an eruption.

Both roles do not contradict the deeper purpose of the observatory. The high-energy universe still has a neutrino pulse to offer the buried receivers.

Solar flares are a bright, repeatable signal until one arrives, across stations powered by the same star.

If you want to learn more about this project, you can check the full study here: Agarwal, S., Aguilar, J. A., Ali, S., Allison, P., Betts, M., Besson, D., … & Zink, A. (2025). Solar flare observations with the radio neutrino observatory greenland (rno-g). Astroparticle physics, 164, 103024.